The present invention relates to a color image recording apparatus to which a developing method is adopted, in which a two-component developer composed of toner and carrier is used, and by which a plurality of color images are recorded. Further, the present invention relates to a toner adhesion amount detecting method by which a desired color reproduction can be easily determined, and to an image forming method by which processing operations according to the results by the detection method are conducted.
In conventional color image recording apparatuses, developing units in which yellow, magenta, cyan and black developers are loaded are provided. In this case, when each color developer is initially loaded in the developing unit, there is a slight difference among toner charging amounts of each developer.
However, in the color image recording apparatus, a developing sleeve and a mixing unit in the developing unit are continuously rotated to simplify control operations, and consumed amounts of color developers are not always uniform but different each other. Therefore, a difference among mixing times of color developers loaded in the developing units occurs during copying operations. Accordingly, a difference in toner charging amounts is caused among developers. The difference in charging amounts exerts a bad influence upon the developing property.
That is, the developing property is due to the force (developing force) which is obtained from the following: the adhesive force (Coulomb's force) of toner and carrier and the adhesive force of developer to a developing sleeve are subtracted from the force due to the electric field caused by an electrostatic latent image.
In this case, there is a tendency that: Coulomb's force is remarkably increased as compared with other forces when a toner charging amount Q/m is increased.
Accordingly, when the toner charging amount is increased, the developing force is decreased. When the toner charging amount is decreased, the developing force is increased. When multi-colors are reproduced, each color can not obtain a desired toner adhesion amount due to the difference of the toner charging amount among color developers, and therefore color balance of a reproduced image is deteriorated, which is a problem.
On the other hand, there is a color image recording apparatus to which an image forming process [hereinafter, called a KNC (Konica New Color) process] is adopted, in which a plurality of toner images are superimposed on a photoreceptor so that a toner image made of plural layers is formed.
The KNC process is conducted in the following manner: charging, exposing and developing processes are repeated on one photoreceptor plural times corresponding to the number of colors so that a toner image composed of a plurality of layers and colors can be formed.
In this case, after the first cycle of charging, exposing and developing processes have been conducted, when charging processes of the second cycle and following cycles are conducted, electric potential after the exposing process is fluctuated due to the toner layer formed on the photoreceptor in the preceding cycle. This is due to the following: exposing light scatters on the surface of toner particles; and it is reflected on the interface of lumps of toner particles, so that the light does not arrive at the surface of the photoreceptor drum under the toner layers. As a result of the foregoing, in the exposing process, the difference of the photoreceptor surface potential is caused between a toner adhered portion and a toner non-adhered portion of the photoreceptor, and therefore, in the second developing process and after that, color phase and density are deviated, which is a problem.
Therefore, when considering the relation between the color toner charging amount and the toner adhesion amount, there is a problem that color balance is unstable from the reason that a desired toner adhesion amount can not be obtained in the KNC process.
On the other hand, conventionally the toner adhesion amount has been detected in the following manner: a reference toner image is individually formed of a plurality of color toners; and each color toner adhesion amount is detected. However, in the foregoing, only whether one color toner image forming conditions are normal or abnormal is detected. In the case where a plurality of color toners are superimposed so that a multi-color image can be formed, when one color toner adhesion amount is normal, and other toner adhesion amounts are abnormal; that is the case when adhesion amounts of all color toners are normal, or when at least some of the color toners are not abnormal, accurate toner image forming conditions can not be determined.
Further, the detection is conducted by a plurality of sensors or by replacing filters, and therefore, the apparatus becomes complicated, so that units or devices can not be disposed around the photoreceptor.
Reference toner images are respectively formed on different positions on the photoreceptor, and therefore, the image forming conditions are not uniform, and accuracy of the toner adhesion amount detection is lowered.
Further, when a plurality of light emitting elements and light receiving elements are used, adjustment for dispersion of light emitting amounts and spectral sensitivity characteristics of the elements are necessary, it takes a long period of time, and the accuracy is lowered.
The object of the present invention is to solve the above-described problems and to provide a color reproduction determination method by which, with respect to a multi-color image which is formed by superimposing a plurality of color toners, whether a desired color reproduction can be obtained or not can be easily determined.
Further, another object of the present invention is to provide an image forming method by which adjustment is conducted so that proper process conditions can be obtained, and preferable color reproduction can be maintained.